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Catechol-''O''-methyltransferase (COMT; ) is one of several enzymes that degrade catecholamines such as dopamine, epinephrine, and norepinephrine. In humans, catechol-''O''-methyltransferase protein is encoded by the COMT gene. As the regulation of catecholamines is impaired in a number of medical conditions, several pharmaceutical drugs target COMT to alter its activity and therefore the availability of catecholamines. COMT was first discovered by the biochemist Julius Axelrod in 1957. == Function == Catechol-''O''-methyltransferase is involved in the inactivation of the catecholamine neurotransmitters (dopamine, epinephrine, and norepinephrine). The enzyme introduces a methyl group to the catecholamine, which is donated by S-adenosyl methionine (SAM). Any compound having a catechol structure, like catecholestrogens and catechol-containing flavonoids, are substrates of COMT. Levodopa, a precursor of catecholamines, is an important substrate of COMT. COMT inhibitors, like entacapone, save levodopa from COMT and prolong the action of levodopa. Entacapone is a widely used adjunct drug of levodopa therapy. When given with an inhibitor of dopa decarboxylase (carbidopa or benserazide), levodopa is optimally saved. This "triple therapy" is becoming a standard in the treatment of Parkinson's disease. Specific reactions catalyzed by COMT include: * Dopamine → 3-Methoxytyramine * DOPAC → HVA (homovanillic acid) * Norepinephrine → Normetanephrine * Epinephrine → Metanephrine * Dihydroxyphenylethylene glycol (DOPEG) → Methoxyhydroxyphenylglycol (MOPEG) * 3,4-Dihydroxymandelic acid (DOMA) → Vanillylmandelic acid (VMA) In the brain, COMT-dependent dopamine degradation is of particular importance in brain regions with low expression of the presynaptic dopamine transporter (DAT), such as the prefrontal cortex. This process is supposed to take place in postsynaptic neurons, as, in general, COMT is located intracellularly in the central nervous system (CNS).〔Schott et al., 2010 http://www.frontiersin.org/molecular_psychiatry/10.3389/fpsyt.2010.00142/abstract〕 COMT can also be found extracellularly, although extracellular COMT plays a less significant role in the CNS than it does peripherally. Despite its importance in neurons, COMT is actually primarily expressed in the liver. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Catechol-O-methyl transferase」の詳細全文を読む スポンサード リンク
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